KUALA LUMPUR, Malaysia — As this Southeast Asian nation mourns the loss of scores of passengers aboard another lost Malaysia Airlines Boeing 777-200, the precautions instituted by the aviation authorities and flight planners to protect commercial aviation along the Russian-Ukrainian border have been shown to be catastrophically insufficient.

The downing of the passenger plane over eastern Ukraine on Thursday occurred shortly after the authorities in Russia and Ukraine, reacting to dangers presented by the conflict around the city of Donetsk, Ukraine, closed air space up to 32,000 feet along the passenger jet’s planned route. Ukraine made the changes on Monday, the same day a Ukrainian AN-26 military cargo plane was destroyed by a missile while flying at 21,000 feet. Russia followed with similar restrictions effective at midnight on Wednesday, hours before Flight 17 took off from Amsterdam.

The decision by government officials to restrict the airspace, rather than close it completely, raised unanswered questions.

The attack on the cargo plane, American and Ukrainian officials said, indicated that a more powerful missile than those previously fired in the conflict had been used. These missiles, including SA-11s, SA-17s and SA-20s, can readily strike aircraft at standard cruising altitudes for commercial passenger jets, changing the nature of the menace to civilian aviation.

But the new restrictions underestimated the risks to a startling degree, aviation officials said, leaving Flight 17 exposed at 33,000 feet to missiles known to fly to more than twice that height. Officials in the United States said on Friday that the jet, with 298 people aboard, was most likely downed by an SA-11, which carries a large high-explosive warhead at roughly three times the speed of sound. Variants of the missile can hit targets at altitudes exceeding 70,000 feet, according to IHS Jane’s, a defense consultancy.

Malaysia Airlines flight dispatchers, who draft flight plans, and the jetliner’s crew, which followed the plan provided to them from Kuala Lumpur, observed the restrictions imposed by Russia and Ukraine, according to European aviation authorities and the airline. One European aviation official, speaking on the condition of anonymity because he was not authorized to discuss the missile strike, said that the airspace restrictions set by Russia and Ukraine were inadequate, but that the airline dispatchers still had the option of plotting routes around the conflict area.

“The general feeling is that if the airspace is closed to 32,000 feet, the last thing I am going to do is fly at 33,000,” he said. “We wouldn’t have gone anywhere near it once we knew they were shooting things out of the sky.”

At a news conference here, Liow Tiong Lai, Malaysia’s transport minister, said the aircraft had been following a safe route that Malaysia Airlines had used for years and that, through Thursday, was still used by several Asian and European airlines. “During that period of time, there are also many other aircraft using the same route,” he said.

Prime Minister Najib Razak of Malaysia pointed out earlier in the day that the International Civil Aviation Organization had kept the flight corridor open, the International Air Transport Association had not restricted travel in Ukrainian airspace, and European air traffic control officials had continued to direct flights through the area. Malaysia Airlines came up with a flight plan within air traffic control parameters, but air traffic control agencies said they did not play an extensive role in evaluating it.

Sergei V. Izvolsky, the spokesman for the Russian Federal Air Transport Agency, said in a telephone interview that it was not up to Russia to give recommendations to foreign air carriers regarding the flight routes for their planes. “They make up their flight plans and coordinate them with their information services,” Mr. Izvolsky said.

Another aviation industry official said that restricting the airspace, rather than closing it, implied that the route was safe even when it was not. “Airlines depend on governments and air traffic control authorities to advise which airspace is available for flight, and they plan within those limits,” Tony Tyler, the director general of the International Air Transport Association in Geneva, said in a statement.

Nico Voorbach, president of the European Cockpit Association, a regional pilot’s union, said: “We have to be able to rely on the information we have from security agencies, governments and national civil aviation authorities. They are normally in a better position to judge if it’s safe.”

Malaysia Airlines issued a statement on Friday saying it had filed a flight plan to cross the area at 35,000 feet, only to be told by Ukrainian air traffic controllers that the plane should maintain an altitude of 33,000 feet. Either elevation was above the restriction, but within range of an SA-11.

A European aviation official confirmed the change to the flight plan. “That was in accordance with normal air traffic control procedures,” said Brian Flynn, the head of network management and external relations at Eurocontrol, the Brussels-based agency that coordinates air traffic in the region. “It would not have been considered unusual.” Based on the radar data, Flight 17 was steady at 33,000 feet at the time of the attack and was on track to stay at that level, Mr. Flynn said.

He said that airspace restrictions had been introduced by Ukraine on July 1, initially restricting flights below 26,000 feet, and had not had much effect on the volume of air traffic over the area, indicating that many carriers considered the route safe. Before June 30, around 400 daily flights passed through the area at all altitudes, he said. After the first set of restrictions, traffic dropped by a few dozen flights per day. When the restriction was extended to 32,000 feet on July 14, the daily traffic decreased only by about 50 flights from a month earlier, a reduction of around 12 percent.

A majority of air traffic crossing the area where Flight 17 was struck consists of international overflights that are already at cruising altitude and would not be required to adjust their normal routes to accommodate the new restrictions.

One aviation official said that complacency among dispatchers may have been an issue in the decision to continue the route. “They plot that same route every single day,” he said.

Malaysian officials said an airline could not be expected to have the intelligence information and other resources to make independent determinations to avoid an area where air traffic controllers were still sending planes. But some carriers had already done just that. China Airlines, the flagship carrier of Taiwan, said that it had avoided flying over all of Ukraine since April 4. Korean Airlines and Asiana Airlines also confirmed that they had not flown planes through Ukrainian airspace since March 3.

Keith Bradsher reported from Kuala Lumpur, C. J. Chivers from the United States, and Nicola Clark from Paris. Matthew L. Wald contributed reporting from New York, and Neil MacFarquhar and Andrew E. Kramer from Moscow.

A version of this article appears in print on , on Page A8 of the New York edition with the headline: Downing of Jet Exposes Defects of Flight Precautions Over Ukraine. Order Reprints | Today’s Paper | Subscribe